In this proposal I wish to use the chicks as an experimental laboratory model to study cellular interaction between bursal cells, thymic dependent lymphocytes and leucocytes comprising the reticuloendothelial system. The interaction between these various cells and their products will be studied in vitro. The leucocytic cells will be from both adult and maturing chickens. The chicken, in contrast to mammals, has anatomically distinct organs, the thymus and bursa of Fabricius, which are necessary for maturation of cellular and humoral immunity. The method involves culturing splenic cells from surgically bursectomized chickens with antigen in vitro for 72 hours. The cell-free supernatant from the splenic cell cultures is added with antigen to suspension cultures of bursal cells which then are stimulated to produce antibody secreting cells. Studies will be carried out to determine if the splenic cell-factor is antigen specific and if it is produced by the adherent or non-adherent cells. The splenic cell-factor also will be used to stimulate bursal and splenic lymphocytes of embryonic and newly hatched chicks to become functional in organ culture prior to the time they normally are. Bursal lymphocytes offer a unique opportunity to evaluate interaction between various leucocytes and also evaluate the effect of cell-free factos of leucocyte cultures. This is because bursal cells in suspension culture do not become antibody secreting cells in the presence of antigen. They, however, are able to respond to antigen with the addition of a small amount of cell-free culture fluid obtained from B-cell deficient, antigen-primed splenic cell cultures. BIBLIOGRAPHIC REFERENCES: Stanisz, M. Hsia, W. Sabet, T., El-Domeiri, A. and Van Alten, P.J., Increased 3H - Thymidine uptake by mitogenically-stimulated, splenic lymphocytes from animals intraperitoneally injected with either Sephadex or Incomplete Freund's Adjuvant. J. Reticuloendothelial Society, 20: 60a (1976). Stanisz, M. and Van Alten P.J., Functional and physical characterization of blastogenic factor isolated from chicken splenic lymphocytes. Fed. Proc., 36: 1308 (1977).